Low Coolant Sensor

I had a issue with what I thought was a bad low coolant sensor. I replaced it with a new sensor, problem solved. Everything worked great. That was last week and now I have the same issue, the warning light and alarm come for low coolant. I have a 1991 Beaver, Cat 3116 250hp. The coolant sensor is located at the bottom of the surge tank. There is plenty of coolant in the surge tank. When I replaced the sensor before it was clean so I don't think dirt or sludge is a problem. I cleaned the wire connection to the sensor before I put it back together. I did not trace the wire backwards and am wondering if wiring maybe be the problem. That is the project for tomorrow. Any suggestions on what else it could be?

Joe